1. Technical Field
The present invention relates to wireless communication, and more particularly, to a method of operating a relay station in a wireless communication system using the relay station.
2. Related Art
IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard provides a technology and protocol for supporting broadband wireless access. IEEE 802.16-2001 had been standardized since 1999 and approved in 2001. This is based on a single carrier physical layer called ‘WirelessMAN-SC’. In IEEE 802.16a standard approved in 2003, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ other than the ‘WirelessMAN-SC’ were further added to the physical layer. After the IEEE 802.16a standard was completed, revised IEEE 802.16-2004 standard was approved in 2004. In order to modify bugs and error of the IEEE 802.16-2004 standard, IEEE 802.16-2004/Cor1 (hereinafter referred to as IEEE 802.16e) was completed in 2005 in the form of ‘corrigendum’.
Today, in a draft by a IEEE 802.16 Task Group j, which is referred to as IEEE 802.16j, a relay station has been introduced and standardized in order to provide coverage extension and throughput enhancement on the basis of the IEEE 802.16e. In the IEEE 802.16j standard, signals can be transferred to a mobile station outside the coverage of a base station through the relay station so as to provide coverage extension. In addition, a channel having high reliability can be provided to a mobile station inside the coverage of a base station. High adaptive modulation and coding (AMC) scheme can be established so as to increase the system capacity.
Relay modes in which a relay station relays signals between a base station and a mobile station include an amplify and forward (AF) mode and a decode and forward (DF) mode. In the AF mode, the relay station amplifies a signal received from a base station or a mobile station and transfers the amplified signal to the mobile station or the base station. In the DF mode, the relay station reproduces information bits from signals received from a base station or a mobile station through processes such as demodulation and decoding, regenerates a signal through processes such as encoding and modulation, and transfers the generated signal to the mobile station or the base station.
The AF mode is advantageous in that time delay taken to transfer signals is short, but disadvantageous in that noise is propagated into or amplified in transferred signals. On the contrary, the DF mode is advantageous in that noise included in signals can be removed and reliability of transferred signals can be increased, but disadvantageous in that time delay taken to transfer signals is long since demodulation and decoding processes are performed.
Accordingly, there is a need for a method of transferring signals using an adequate relay mode depending on conditions.